Improved measurements of the branching fractions for B0 → π+π− and B0 → K+π−, and a search for B0 → K+K−

Abstract

We present measurements of the branching fractions for the charmless two-body decays B 0 → π + π − and B 0 → K + π − , and a search for the decay B 0 → K + K − . We include the effects of final-state radiation from the daughter mesons for the first time, and quote branching fractions for the inclusive processes B 0 → h + h ' − n γ , where h and h ′ are pions or kaons. The maximum value of the sum of the energies of the n undetected photons, E max  γ , is mode-dependent. Using a data sample of approximately 227 × 10 6 Υ ( 4 S ) → B ¯¯¯ B decays collected with the BABAR detector at the PEP-II asymmetric-energy e + e − collider at SLAC, we measure: B ( B 0 → π + π − n γ ; E max  γ = 150 MeV ) = ( 5.1 ± 0.4 ± 0.2 ) × 10 − 6 , B ( B 0 → K + π − n γ ; E max  γ = 105 MeV ) = ( 18.1 ± 0.6 ± 0.6 ) × 10 − 6 , B ( B 0 → K + K − n γ ; E max  γ = 59 MeV ) < 0.5 × 10 − 6 ( 90 % confidence level ) , where the first uncertainty is statistical and the second is systematic. Theoretical calculations can be used to extrapolate from the above measurements the nonradiative branching fractions, B 0 . Using one such calculation, we find: B 0 ( B 0 → π + π − ) = ( 5.5 ± 0.4 ± 0.3 ) × 10 − 6 , B 0 ( B 0 → K + π − ) = ( 19.1 ± 0.6 ± 0.6 ) × 10 − 6 , B 0 ( B 0 → K + K − ) < 0.5 × 10 − 6 ( 90 % confidence level ) . Meaningful comparison between theory and experiment, as well as combination of measurements from different experiments, can be performed only in terms of these nonradiative quantities.